Progressive expression of vascular endothelial growth factor (VEGF) and angiogenesis after chronic ischemic hypoperfusion in rat

Association of Carotid Artery Disease with Collateralization and Infarct Growth in Patients with Acute Middle Cerebral Artery Occlusion

BACKGROUND AND PURPOSE

Collaterals are important in large vessel occlusions (LVO), but the role of carotid artery disease (CAD) in this context remains unclear. This study aimed to investigate the impact of CAD on intracranial collateralization and infarct growth after thrombectomy in LVO.

MATERIALS AND METHODS

All patients who underwent thrombectomy due to M1 segment occlusion from 01/2015 to 12/2021 were retrospectively included. Internal carotid artery stenosis according to NASCET was assessed on the affected and nonaffected sides. Collaterals were assessed according to the Tan score. Infarct growth was quantified by comparing ASPECTS on follow-up imaging with baseline ASPECTS.

RESULTS

In total, 709 patients were included, 118 (16.6%) of whom presented with CAD (defined as severe stenosis ≥70% or occlusion ipsilaterally), with 42 cases (5.9%) being contralateral. Good collateralization (Tan 3) was present in 56.5% of the patients with ipsilateral CAD and 69.1% of the patients with contralateral CAD. The ipsilateral stenosis grade was an independent predictor of good collateral supply (adjusted OR: 1.01; NASCET point, 95% CI: 1.00-1.01; P = .009), whereas the contralateral stenosis grade was not (P = .34). Patients with ipsilateral stenosis of ≥70% showed less infarct growth (median ASPECTS decay: 1; IQR: 0-2) compared with patients with 0%-69% stenosis (median: 2; IQR: 1-3) (P = .005). However, baseline ASPECTS was significantly lower in patients with stenosis of 70%-100% (P < .001). The results of a multivariate analysis revealed that increasing ipsilateral stenosis grade (adjusted OR: 1.0; 95% CI: 0.99-1.00; P = .004) and good collateralization (adjusted OR: 0.5; 95% CI: 0.4-0.62; P < .001) were associated with less infarct growth.

CONCLUSIONS

CAD of the ipsilateral ICA is an independent predictor of good collateral supply. Patients with CAD tend to have larger baseline infarct size but less infarct growth.

Experimental Animal Models for Moyamoya Disease: A Species-Oriented Scoping Review

Moyamoya disease (MMD) is a rare cerebrovascular disease characterized by progressive stenosis of large intracranial arteries and a hazy network of basal collaterals called moyamoya vessels. The etiology and pathogenesis of MMD are still obscure. The biggest obstacles in the basic research of MMD are difficulty in obtaining specimens and the lack of an animal model. It is necessary to use appropriate and rationally designed animal models for the correct evaluation. Several animal models and methods have been developed to produce an effective MMD model, such as zebrafish, mice and rats, rabbits, primates, felines, canines, and peripheral blood cells, each with advantages and disadvantages. There are three mechanisms for developing animal models, including genetic, immunological/inflammatory, and ischemic animal models. This review aims to analyze the characteristics of currently available models, providing an overview of the animal models framework and the convenience of selecting model types for MMD research. It will be a great benefit to identify strategies for future model generations.

Experimental animal models for moyamoya disease and treatment: a pathogenesis-oriented scoping review

OBJECTIVE

Moyamoya disease (MMD) is an intracranial steno-occlusive pathology characterized by progressive narrowing of proximal large vessels, including the terminal internal carotid arteries (ICAs), middle cerebral arteries, or anterior cerebral arteries. Named for the "puff of smoke" appearance of the anomalous vascularization visualized on cerebral angiography, MMD lacks a well-defined etiology, although significant insights have been made, including the identification of a susceptibility gene, RNF213, in humans with the disease. A limitation to advancing the understanding and treatment of MMD has been the lack of experimental animal models that authentically reflect the clinical pathogenesis. In an effort to analyze characteristics of currently available models and identify strategies for future model generation, the authors performed a scoping review of experimental animal models that have been used to study MMD.

METHODS

A systematic search of PubMed, Web of Science, and Scopus was performed to identify articles describing animal models used to study MMD. Additional articles were identified via citation searching. Study selection and data extraction were performed by two independent reviewers based on defined inclusion and exclusion criteria.

RESULTS

A total of 44 articles were included for full-text review. The methods used to generate these animal models were broadly classified as surgical (n = 25, 56.8%), immunological (n = 7, 15.9%), genetic (n = 6, 13.6%), or a combination (n = 6, 13.6%). Surgical models typically involved permanent ligation of one or both of the common carotid arteries or ICAs to produce chronic cerebral hypoperfusion. Genetic models utilized known MMD or cerebrovascular disease-related genes, such as RNF213 or ACTA2, to induce heritable cerebral vasculopathy. Finally, immunological models attempted to induce vasculitis-type pathology by recapitulating the inflammatory milieu thought to underlie MMD.

CONCLUSIONS

Models generated for MMD have involved three general approaches: surgical, immunological, and genetic. Although each reflects a key aspect of MMD pathogenesis, the failure of any individual model to recapitulate the development, progression, and consequences of the disease underscores the importance of future work in developing a multietiology model.

Methylene Blue Preserves Cytochrome Oxidase Activity and Prevents Neurodegeneration and Memory Impairment in Rats With Chronic Cerebral Hypoperfusion

Chronic cerebral hypoperfusion in neurocognitive disorders diminishes cytochrome oxidase activity leading to neurodegenerative effects and impairment of learning and memory. Methylene blue at low doses stimulates cytochrome oxidase activity and may thus counteract the adverse effects of cerebral hypoperfusion. However, the effects of methylene blue on cytochrome oxidase activity during chronic cerebral hypoperfusion have not been described before. To test this hypothesis, rats underwent bilateral carotid artery occlusion or sham surgery, received daily 4 mg/kg methylene blue or saline injections, and learned a visual water task. Brain mapping of cytochrome oxidase activity was done by quantitative enzyme histochemistry. Permanent carotid occlusion for 1 month resulted in decreased cytochrome oxidase activity in visual cortex, prefrontal cortex, perirhinal cortex, hippocampus and amygdala, and weaker interregional correlation of cytochrome oxidase activity between these regions. Methylene blue preserved cytochrome oxidase activity in regions affected by carotid occlusion and strengthened their interregional correlations of cytochrome oxidase activity, which prevented neurodegenerative effects and facilitated task-specific learning and memory. Brain-behavior correlations revealed positive correlations between performance and brain regions in which cytochrome oxidase activity was preserved by methylene blue. These results are the first to demonstrate that methylene blue prevents neurodegeneration and memory impairment by preserving cytochrome oxidase activity and interregional correlation of cytochrome oxidase activity in brain regions susceptible to chronic hypoperfusion. This demonstration provides further support for the hypothesis that lower cerebral blood flow results in an Alzheimer's-like syndrome and that stimulating cytochrome oxidase activity with low-dose methylene blue is neuroprotective.

Brain Microvascular Pericytes in Vascular Cognitive Impairment and Dementia

Pericytes are unique, multi-functional mural cells localized at the abluminal side of the perivascular space in microvessels. Originally discovered in 19th century, pericytes had drawn less attention until decades ago mainly due to lack of specific markers. Recently, however, a growing body of evidence has revealed that pericytes play various important roles: development and maintenance of blood–brain barrier (BBB), regulation of the neurovascular system (e.g., vascular stability, vessel formation, cerebral blood flow, etc.), trafficking of inflammatory cells, clearance of toxic waste products from the brain, and acquisition of stem cell-like properties. In the neurovascular unit, pericytes perform these functions through coordinated crosstalk with neighboring cells including endothelial, glial, and neuronal cells. Dysfunction of pericytes contribute to a wide variety of diseases that lead to cognitive impairments such as cerebral small vessel disease (SVD), acute stroke, Alzheimer’s disease (AD), and other neurological disorders. For instance, in SVDs, pericyte degeneration leads to microvessel instability and demyelination while in stroke, pericyte constriction after ischemia causes a no-reflow phenomenon in brain capillaries. In AD, which shares some common risk factors with vascular dementia, reduction in pericyte coverage and subsequent microvascular impairments are observed in association with white matter attenuation and contribute to impaired cognition. Pericyte loss causes BBB-breakdown, which stagnates amyloid β clearance and the leakage of neurotoxic molecules into the brain parenchyma. In this review, we first summarize the characteristics of brain microvessel pericytes, and their roles in the central nervous system. Then, we focus on how dysfunctional pericytes contribute to the pathogenesis of vascular cognitive impairment including cerebral ‘small vessel’ and ‘large vessel’ diseases, as well as AD. Finally, we discuss therapeutic implications for these disorders by targeting pericytes.

Chronic cerebral hypoperfusion: An undefined, relevant entity

Despite the large body of data available, chronic cerebral hypoperfusion lacks an operative definition. In a tautological way, the term hypoperfusion is being referred to conditions of "inadequate blood flow", "defects of perfusion" or "dysfunction of autoregulation". The chronicity refers to sustained conditions or wavering states characterized by repeated phases of inefficient functional hyperemia. The phenomenon may affect the whole brain or defined areas. A few defined clinical disorders, including heart failure, hypotension, atherosclerosis of large or small vessels and carotid stenosis are thought to cause progressive brain disorders due to chronic hypoperfusion. The clinical relevance manifests mostly as neurocognitive disorders associated with neuroimaging changes.The available data support a conceptual framework that considerschronic cerebral hypoperfusiona likely, relevant pathogenic mechanism for the neurodegeneration-like progression of the neurocognitive disorders. The relationship between neuropathology, cerebral perfusion, and symptoms progression is, however, elusive for several aspects. Typical microangiopathy findings, such as MRI white matter hyperintensities, may appear in individuals without any cerebrovascular risk or vascular lesions. Pathology features of the MRI changes, such as demyelination and gliosis, may result from dysfunction of the neuro-vascular unit not directly associated withvascular mechanisms. In this review, we aim to overview the most common clinical conditions thought to reflect chronic hypoperfusion.

A Novel Octapeptide Derived From G Protein-Coupled Receptor 124 Improves Cognitive Function Via Pro-Angiogenesis In A Rat Model Of Chronic Cerebral Hypoperfusion-Induced Vascular Dementia

PURPOSE

The lack of effective therapies mandates the development of new treatment strategies for vascular dementia (VaD). G protein-coupled receptor 124 (GPR124) may be a therapeutic target for angiogenesis-related diseases of CNS, including VaD. The GCPF peptide is a truncated and screened fragment of the GPR124 extracellular domain. The potential use of GCPF for VaD treatment, angiogenesis and targeting of integrin αvβ3 are evaluated.

METHODS AND RESULTS

First, the in vivo results indicated that the GCPF peptide could decrease mean escape latency and increase platform crossing times in BCCAO rats. Second, the in vitro and ex vivo results indicated that the GCPF peptide was an active angiogenic peptide and could promote hCMEC/D3 cell migration and adhesion to ECM molecules. Third, in silico analyses predicted that GCPF could specifically interact with integrin αvβ3; the ∆G of GCPF binding to the binding pocket was -16.402 KJ/mol. The molecular characteristics indicated that highly hydrophilic GCPF with a pI of 11.70 had a short half-life in mammals (~1 hr). Finally, the ELISA experiments indicated that low dissociation constant (Kd= 2.412±0.455 nM) corresponds to the high affinity of GCPF for integrin αvβ3.

CONCLUSION

The data indicate that adhesion of GCPF immobilized on ECM surface to endothelial cells via integrin αvβ3 modulates cellular functions to promote angiogenesis and improve cognitive function. This is the first report to prove that GCPF, a novel octapeptide, may be an effective strategy for VaD therapy.

A cortical microvascular structure in vascular dementia, Alzheimer's disease, frontotemporal lobar degeneration and nondemented controls: a sign of angiogenesis due to brain ischaemia?

Aims

We observed a microvascular structure in the cerebral cortex that has not, to our knowledge, been previously described. We have termed the structure a ‘raspberry’, referring to its appearance under a bright‐field microscope. We hypothesized that raspberries form through angiogenesis due to some form of brain ischaemia or hypoperfusion. The aims of this study were to quantify raspberry frequency within the cerebral cortex according to diagnosis (vascular dementia, Alzheimer's disease, frontotemporal lobar degeneration and nondemented controls) and brain regions (frontal, temporal, parietal and occipital cortices, regardless of diagnosis).

Materials and methods

In each of 10 age‐matched subjects per group, a 20‐mm section of the cerebral cortex was examined in haematoxylin‐and‐eosin‐stained sections of the frontal, temporal and parietal, and/or occipital lobes. Tests were performed to validate the haematoxylin‐and‐eosin‐based identification of relative differences between the groups, and to investigate inter‐rater variability.

Results

Raspberry frequency was highest in subjects with vascular dementia, followed by those with frontotemporal lobar degeneration, Alzheimer's disease and last, nondemented controls. The frequency of raspberries in subjects with vascular dementia differed from that of all other groups at a statistically significant level. In the cerebral lobes, there was a statistically significant difference between the frontal and occipital cortices.

Conclusions

We believe the results support the hypothesis that raspberries are a sign of angiogenesis in the adult brain. It is pertinent to discuss possible proangiogenic stimuli, including brain ischaemia (such as mild hypoperfusion due to a combination of small vessel disease and transient hypotension), neuroinflammation and protein pathology.

Chronic Cerebral Hypoperfusion Induces Alterations of Matrix Metalloproteinase-9 and Angiopoietin-2 Levels in the Rat Hippocampus

Angiogenic factors contribute to cerebral angiogenesis following cerebral hypoperfusion, and understanding these temporal changes is essential to developing effective treatments. The present study examined temporal alterations in angiogenesis-related matrix metalloproteinase-9 (MMP-9) and angiopoietin-2 (ANG-2) expression in the hippocampus following bilateral common carotid artery occlusion (BCCAo). Male Wistar rats (12 weeks of age) were randomly assigned to sham-operated control or experimental groups, and expression levels of MMP-9 and ANG-2 were assessed after BCCAo (1 week, 4 weeks, and 8 weeks), using western blotting. Protein expression increased 1 week after BCCAo and returned to control levels at 4 and 8 weeks. In addition, immunofluorescence staining demonstrated that the MMP-9- and ANG-2-positive signals were primarily observed in the NeuN-positive neurons with very little labeling in non-neuronal cells and no labeling in endothelial cells. In addition, these cellular locations of MMP-9- and ANG-2-positive signals were not altered over time following BCCAo. Other angiogenic factors such as vascular endothelial growth factor and hypoxia-inducible factor did not differ from controls at 1 week; however, expression of both factors increased at 4 and 8 weeks in the BCCAo group compared to the control group. Our findings increase understanding of alterations in angiogenic factors during the progression of cerebral angiogenesis and are relevant to developing effective temporally based therapeutic strategies for chronic cerebral hypoperfusion-associated neurological disorders such as vascular dementia.

MicroRNA-26b Regulates the Microglial Inflammatory Response in Hypoxia/Ischemia and Affects the Development of Vascular Cognitive Impairment

Background: Microglia play an important role in the central nervous system as immune cells and are often activated by post-ischemic injury. MicroRNAs are small endogenous RNAs affecting many complex cellular biological functions that are involved in neurodegenerative and cerebrovascular diseases. Previous studies have shown that microRNA-26b (miR-26b) is downregulated in BV-2 cells exposed to oxygen-glucose deprivation (OGD).

Objective: This study aimed to investigate how miR-26b regulates microglial activation and its neurotoxicity as well as the effect of miR-26b on vascular cognitive impairment (VCI).

Methods: Here, we used PCR to detect the mRNA expression of miR-26b and cytokines, western blot for the protein expression of cytokines, and the live/dead assay for neuronal apoptosis. In addition, we employed a luciferase assay to identify the possible target genes of miR-26b. Furthermore, we studied the effects of cerebral ischemia by bilateral common carotid artery occlusion (BCCAO) in rats. We used staining to identify neurons and microglia, and we tested cognitive function by the T-maze test.

Results: Our results showed that OGD activated microglia and increased the expression of interleukin (IL)-6 and other cytokines. Similarly, BCCAO activated microglia and increased the expression of IL-6 in the hippocampal CA1 area. We further found that miR-26b decreased the number of activated microglia and targeted IL-6. Moreover, miR-26b expression attenuated microglial activation, inflammation, neurotoxicity and VCI.

Conclusion: Our results suggested that miR-26b is involved in microglial activation and neurotoxicity in hypoxia/ischemia via IL-6. Therefore, increasing miR-26b expression may improve cognitive function.

Common Carotid Arteries Occlusion Surgery in Adult Rats as a Model of Chronic Cerebral Hypoperfusion

Chronic cerebral hypoperfusion (CCH) is an important risk factor of vascular dementia (VaD) and Alzheimer's disease (AD). Hypoxia/ischemia in the whole brain induced by CCH causes serious damage to brain structure and function, which can lead to cognitive impairment. Two-vessel occlusion (2-VO), also known as permanent, bilateral common carotid artery occlusion, is one of the most widely used animal models (e.g., rat) of CCH to investigate the mechanisms of neurodegenerative processes. In this protocol, we present the surgical procedure for 2-VO in rats.

The neuron-astrocyte-microglia triad in CA3 after chronic cerebral hypoperfusion in the rat: Protective effect of dipyridamole

We investigated the quantitative and morphofunctional alterations of neuron-astrocyte-microglia triads in CA3 hippocampus, in comparison to CA1, after 2 Vessel Occlusion (2VO) and the protective effect of dipyridamole. We evaluated 3 experimental groups: sham-operated rats (sham, n=15), 2VO-operated rats treated with vehicle (2VO-vehicle, n=15), and 2VO-operated rats treated with dipyridamole from day 0 to day 7 (2VO-dipyridamole, n=15), 90days after 2VO. We analyzed Stratum Pyramidalis (SP), Stratum Lucidum (SL) and Stratum Radiatum (SR) of CA3. 1) ectopic neurons increased in SL and SR of 2VO-vehicle, and 2VO-dipyridamole rats; 2) apoptotic neurons increased in SP of 2VO-vehicle rats and dipyridamole reverted this effect; 3) astrocytes increased in SP, SL and SR of 2VO-vehicle and 2VO-dipyridamole rats; 4) TNF-α expression increased in astrocytes, blocked by dipyridamole, and in dendrites in SR of 2VO-vehicle rats; 5) total microglia increased in SL and SR of 2VO-vehicle and 2VO-dipyridamole rats; 6) triads increased in SR of 2VO-vehicle rats and dipyridamole reverted this effect. Microglia cooperated with astrocytes to phagocytosis of apoptotic neurons and debris, and engulfed ectopic non-fragmented neurons in SL of 2VO-vehicle and 2VO-dipyridamole rats, through a new mechanism called phagoptosis. CA3 showed a better adaptive capacity than CA1 to the ischemic insult, possibly due to the different behaviour of astrocytes and microglial cells. Dipyridamole had neuroprotective effects.

Combined therapy (intravitreal bevacizumab plus verteporfin photodynamic therapy) versus intravitreal bevacizumab monotherapy for choroidal neovascularization due to age-related macular degeneration: a 1-year follow-up study

PURPOSE

To assess the efficacy and safety of combined intravitreal bevacizumab and low-fluency-rate photodynamic therapy (PDT) in the treatment of choroidal neovascularization (CNV) associated with age-related macular degeneration (AMD) and to compare it with intravitreal bevacizumab monotherapy.

METHODS

A total of 62 eyes of 62 patients with angiographic evidence of CNV were divided into 2 groups: the eyes of one group were treated with a combined therapy of 1 intravitreal bevacizumab injection (1.25 mg) and PDT within 7 days; the eyes of the other group received intravitreal bevacizumab monotherapy. Clinical evidence of complications, best-corrected visual acuity (BVCA) and fluorescein leakage were evaluated. Best-corrected visual acuity and optical coherence tomography (OCT) were tested monthly and followed for 12 months.

RESULTS

In the combined group the mean BCVA increased from 0.61 logMAR before the treatment to 0.54 logMAR at 12 months' follow-up. In the monotherapy group the mean BCVA increased from 0.65 logMAR to 0.60 logMAR at 12 months' follow-up. There was no significant difference in visual acuity outcomes between groups (P > 0.05). In the combined group the mean number of treatments was 1.19 per patient; in the monotherapy group, 5.31 per patient (P < 0.01).

CONCLUSIONS

Combined therapy appears to be an effective option for CNV associated with AMD treatment allowing a significant reduction of intravitreal injections.

Investigation of redox status in chronic cerebral hypoperfusion-induced neurodegeneration in rats

Aging related reduction in cerebral blood flow (CBF) has been linked with neurodegenerative disorders including Alzheimer's disease and dementia. Experimentally, a condition of chronic cerebral hypoperfusion due to reduced CBF can be induced by permanent bilateral occlusion of common carotid arteries (2-vessel occlusion, 2VO) in rats. Since oxidative stress, leading to neuronal apoptosis and death, is one of the mechanisms, which is thought to play a significant role in chronic degenerative neurological disorders, the present study was planned to assess the ROS status by measuring the levels of anti-oxidant enzymes that might occur during chronic cerebral hypoperfusion. Antioxidant enzymes namely glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase were measured in the brain tissue at eight weeks of 2VO induction in rats. Results show significantly elevated levels of GPx, SOD, and catalase enzymes as compared with the control group. It is possible that compensatory rise in antioxidant enzymes occurs in response to increased oxidative stress following ischemic insult.

Ameliorating the effect of astragaloside IV on learning and memory deficit after chronic cerebral hypoperfusion in rats

Astragaloside IV (AS-IV) has been reported to have a prominent antioxidant effect and was proposed as a promising agent for the prevention of neurodegenerative disorders accompanied by cognitive impairment. The present study investigated the ameliorating effect of AS-IV on learning and memory deficits induced by chronic cerebral hypoperfusion in rats. Rats were treated with two doses of AS-IV (10 and 20 mg/kg, i.p.) daily for 28 days starting from the 5th week after permanent bilateral common carotid artery occlusion. AS-IV treatment (at dose of 20 mg/kg) significantly improved the spatial learning and memory deficits assessed using the Morris water maze test in rats with chronic cerebral hypoperfusion. AS-IV significantly attenuated neuronal apoptosis as well as the levels of superoxide dismutase and lipid peroxidation markers, including malondialdehyde and 4-hydroxy-2-nonenal, in the hippocampus. AS-IV also significantly reduced 8-hydroxy-2’-deoxyguanosine expression, a maker of oxidative DNA damage, while significantly inhibited the astrocyte and microglia activation in the hippocampus. The results indicate that AS-IV has therapeutic potential for the prevention of dementia caused by cerebral hypoperfusion and suggest that the ameliorating effect of AS-IV on learning and memory deficits might be the result of suppressing neuronal apoptosis and oxidative damage in the hippocampus.

The neuron-astrocyte-microglia triad in a rat model of chronic cerebral hypoperfusion: protective effect of dipyridamole

Chronic cerebral hypoperfusion during aging may cause progressive neurodegeneration as ischemic conditions persist. Proper functioning of the interplay between neurons and glia is fundamental for the functional organization of the brain. The aim of our research was to study the pathophysiological mechanisms, and particularly the derangement of the interplay between neurons and astrocytes-microglia with the formation of "triads," in a model of chronic cerebral hypoperfusion induced by the two-vessel occlusion (2VO) in adult Wistar rats (n = 15). The protective effect of dipyridamole given during the early phases after 2VO (4 mg/kg/day i.v., the first 7 days after 2VO) was verified (n = 15). Sham-operated rats (n = 15) were used as controls. Immunofluorescent triple staining of neurons (NeuN), astrocytes (GFAP), and microglia (IBA1) was performed 90 days after 2VO. We found significantly higher amount of "ectopic" neurons, neuronal debris and apoptotic neurons in CA1 Str. Radiatum and Str. Pyramidale of 2VO rats. In CA1 Str. Radiatum of 2VO rats the amount of astrocytes (cells/mm(2)) did not increase. In some instances several astrocytes surrounded ectopic neurons and formed a "micro scar" around them. Astrocyte branches could infiltrate the cell body of ectopic neurons, and, together with activated microglia cells formed the "triads." In the triad, significantly more numerous in CA1 Str. Radiatum of 2VO than in sham rats, astrocytes and microglia cooperated in the phagocytosis of ectopic neurons. These events might be common mechanisms underlying many neurodegenerative processes. The frequency to which they appear might depend upon, or might be the cause of, the burden and severity of neurodegeneration. Dypiridamole significantly reverted all the above described events. The protective effect of chronic administration of dipyridamole might be a consequence of its vasodilatory, antioxidant and anti-inflammatory role during the early phases after 2VO.

Long-term vision and non-vision dominant behavioral deficits in the 2-VO rats are accompanied by time and regional glial activation in the white matter

The permanent occlusion of common carotid arteries (2-VO) in rats has been shown to induce progressive and long-lasting deficits in cognitive performance, however, whether these aberrant behaviors are attributed to visual dysfunction or cognitive impairment and what are the underlying mechanisms, remain controversial. In the present study, vision dominant (Morris water maze) and non-vision dominant (voice-cued fear conditioning) behavioral tests were assigned to comprehensively evaluate the influence of 2-VO lesion on cognitive behaviors. In the Morris water maze test, escape latencies of 2-VO rats were markedly increased in both hidden and unfixed visible platform tasks, which were accompanied by severe retinal damage. In the voice-cued fear conditioning test, significant reduction in the percentage of freezing behavior was observed at 60 days after 2-VO lesion. Chronic lesion by 2-VO failed to cause noticeable changes in the grey matter, as indicated by intact hippocampal and prefrontal cortical structures, sustained synaptic protein levels and glial cell numbers. In contrast, aberrant arrangement of myelinated axons was observed in the optic tract, but not in the corpus callosum and inner capsule of 2-VO rats. Concurrently, marked astrocyte proliferation and microglia activation in the optic tract occurred at 3 days after 2-VO lesion, and continued for up to 60 days. Differently, robust glial activation was observed in the corpus callosum at 3 days after 2-VO surgery, and then gradually returned to the baseline level at 14 and 60 days. Our study reported for the first time about the effect of 2-VO on the long-term cognitive impairment in the non-vision dominant fear conditioning test, which may be more applicable than the Morris water maze test for assessing 2-VO associated cognitive function. The time and region specific glial activation in the white matter may relate to retinal impairment, even behavioral deficits, in the setting of chronic cerebral hypoperfusion.

Pathophysiology of white matter perfusion in Alzheimer's disease and vascular dementia

The pathophysiology of white matter hypoperfusion is poorly understood. Barker et al. quantify ante-mortem hypoperfusion by measuring myelin proteins differentially susceptible to ischaemia, and assess the extent to which vasoregulatory factors protect from or contribute to ischaemic white matter injury in Alzheimer’s disease and vascular dementia.

Little is known about the contributors and physiological responses to white matter hypoperfusion in the human brain. We previously showed the ratio of myelin-associated glycoprotein to proteolipid protein 1 in post-mortem human brain tissue correlates with the degree of ante-mortem ischaemia. In age-matched post-mortem cohorts of Alzheimer’s disease (n = 49), vascular dementia (n = 17) and control brains (n = 33) from the South West Dementia Brain Bank (Bristol), we have now examined the relationship between the ratio of myelin-associated glycoprotein to proteolipid protein 1 and several other proteins involved in regulating white matter vascularity and blood flow. Across the three cohorts, white matter perfusion, indicated by the ratio of myelin-associated glycoprotein to proteolipid protein 1, correlated positively with the concentration of the vasoconstrictor, endothelin 1 (P = 0.0005), and negatively with the concentration of the pro-angiogenic protein, vascular endothelial growth factor (P = 0.0015). The activity of angiotensin-converting enzyme, which catalyses production of the vasoconstrictor angiotensin II was not altered. In samples of frontal white matter from an independent (Oxford, UK) cohort of post-mortem brains (n = 74), we confirmed the significant correlations between the ratio of myelin-associated glycoprotein to proteolipid protein 1 and both endothelin 1 and vascular endothelial growth factor. We also assessed microvessel density in the Bristol (UK) samples, by measurement of factor VIII-related antigen, which we showed to correlate with immunohistochemical measurements of vessel density, and found factor VIII-related antigen levels to correlate with the level of vascular endothelial growth factor (P = 0.0487), suggesting that upregulation of vascular endothelial growth factor tends to increase vessel density in the white matter. We propose that downregulation of endothelin 1 and upregulation of vascular endothelial growth factor in the context of reduced ratio of myelin-associated glycoprotein to proteolipid protein 1 are likely to be protective physiological responses to reduced white matter perfusion. Further analysis of the Bristol cohort showed that endothelin 1 was reduced in the white matter in Alzheimer’s disease (P < 0.05) compared with control subjects, but not in vascular dementia, in which endothelin 1 tended to be elevated, perhaps reflecting abnormal regulation of white matter perfusion in vascular dementia. Our findings demonstrate the potential of post-mortem measurement of myelin proteins and mediators of vascular function, to assess physiological and pathological processes involved in the regulation of cerebral perfusion in Alzheimer’s disease and vascular dementia.

Neurovascular abnormalities in brain disorders: highlights with angiogenesis and magnetic resonance imaging studies

The coupling between neuronal activity and vascular responses is controlled by the neurovascular unit (NVU), which comprises multiple cell types. Many different types of dysfunction in these cells may impair the proper control of vascular responses by the NVU. Magnetic resonance imaging, which is the most powerful tool available to investigate neurovascular structures or functions, will be discussed in the present article in relation to its applications and discoveries. Because aberrant angiogenesis and vascular remodeling have been increasingly reported as being implicated in brain pathogenesis, this review article will refer to this hallmark event when suitable.

Down-regulation of IGF-1/IGF-1R in hippocampus of rats with vascular dementia

Insulin-like growth factor-1 (IGF-1) has been demonstrated to have neuroprotective effects, but little is known concerning its role in vascular dementia (VaD). This study aimed to evaluate expression of IGF-1 signaling in hippocampus in rat model of VaD, and probe the underlying mechanisms. Permanent occlusion of bilateral common carotid arteries (2-VO) was used as VaD model. Learning and memory functions were declined significantly in 2-VO rats, and these impairments were further deteriorated with the prolongation of 2-VO treatment. IGF-1, IGF-1 receptor (IGF-1R), total Akt and phosphorylated Akt (p-Akt) were all measured at 1, 2 and 4 months following 2-VO injury. Compared with controls, IGF-1, IGF-1 mRNA and p-Akt expression were significantly decreased in hippocampus of 2-VO rats. However, changes of IGF-1R and total Akt levels were not significant. These results suggest that down-regulation of IGF-1 and p-Akt may contribute to the impairments of learning and memory functions after 2-VO. IGF-1/IGF-1R signaling system may involved in the onset and development of VaD.

Serial expression of hypoxia inducible factor-1α and neuronal apoptosis in hippocampus of rats with chronic ischemic brain

OBJECTIVE

The purpose of this study is to investigate serial changes of hypoxia-inducible factor 1α (HIF-1α), as a key regulator of hypoxic ischemia, and apoptosis of hippocampus induced by bilateral carotid arteries occlusion (BCAO) in rats.

METHODS

Adult male Wistar rats were subjected to the permanent BCAO. The time points studied were 1, 2, 4, 8, and 12 weeks after occlusions, with n=6 animals subjected to BCAO, and n=2 to sham operation at each time point, and brains were fixed by intracardiac perfusion fixation with 4% neutral-buffered praraformaldehyde for brain section preparation. Immunohistochemistry (IHC), western blot and terminal uridine deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay were performed to evaluate HIF-1α expression and apoptosis.

RESULTS

In IHC and western blot, HIF-1α levels were found to reach the peak at the 2nd week in the hippocampus, while apoptotic neurons, in TUNEL assay, were maximal at the 4th week in the hippocampus, especially in the cornu ammonis 1 (CA1) region. HIF-1α levels and apoptosis were found to fluctuate during the time course.

CONCLUSION

This study showed that BCAO induces acute ischemic responses for about 4 weeks then chronic ischemia in the hippocampus. These in vivo data are the first to show the temporal sequence of apoptosis and HIF-1α expression.

Dynamics of dystroglycan complex proteins and laminin changes due to angiogenesis in rat cerebral hypoperfusion

Permanent bilateral carotid occlusion is a well known cerebral hypoperfusion model in rats. The aim of our study was to investigate the different stages of vascular reaction by detecting changes in the extracellular martix proteins and to examine their relationship to angiogenesis after occlusion. Experiments were performed on adult male rats. Brain samples were investigated from day 1 to day 30 post-surgery. Immunohistochemical analysis was performed on the whole hippocampus and on the adjacent cortex in order to investigate extracellular martix proteins, such as the markers of dystroglycan complex (β-dystroglycan, α-dystrobrevin and utrophin) and a marker of basal lamina (laminin). The levels of the proteins were estimated by western blot analysis. Vascular density as well as blood-brain barrier permeability were studied on brain slices from the same regions. Our results showed altered laminin and β-dystroglycan immunoreactivity beginning 2 days after the onset of occlusion followed by an increased utrophin immunoreactivity without blood-brain barrier disruption 5 days later. By day 30 of hypoperfusion, when increased vascular density was detected, all changes returned to baseline levels. Western blot analysis showed significant differences in β-dystroglycan and utrophin expression. Our results indicate that the different stages of neovascularisation resulting from cerebral hypoperfusion can be well defined by the markers laminin, β-dystroglycan, and utrophin and that these markers are more likely to correlate with glio-vascular decoupling than does altered blood-brain barrier function.

Mannosylated liposomal cytidine 5' diphosphocholine prevent age related global moderate cerebral ischemia reperfusion induced mitochondrial cytochrome c release in aged rat brain

Mitochondrial dysfunctions generating from cerebral ischemia-reperfusion exert a potential threat on neuronal cell survival and hence, accelerate the aging process and age dependent neuropathology. Thirty min moderate cerebral ischemia induced by bilateral common carotid artery occlusion (BCCAO) followed by 30 min reperfusion caused an increased diene production, depleted glutathione (GSH) content, reduced superoxide dismutase (SOD) and catalase activities and pyramidal neuronal loss in young (2 months old) and aged (20 months old) rat brain compared to sham operated controls. Cytidine 5' diphosphocholine (CDP-Choline) is a known neuroprotective drug. CDP-Choline after metabolism in the liver suffers hydrolysis and splits into cytidine and choline before entering systemic circulation and hardly circumvents blood brain barrier (BBB) as such. Previous reports show CDP-Choline liposomes significantly increased in vivo uptake compared to "free drug" administration in cerebral ischemia. To enhance the therapeutic concentration build up in brain we sought to formulate mannosylated liposomal CDP-Choline (MLCDP) utilizing the mannose receptors. We tested the therapeutic supremacy of MLCDP over liposomal CDP-Choline (LCDP) in global moderate cerebral ischemia reperfusion induced neuronal damage. CDP-Choline in MLCDP delivery system was found potent to exert substantial protection against global moderate cerebral ischemia reperfusion induced mitochondrial damage in aged rat brain. Membrane lipid peroxidation, GSSG/GSH ratio and reactive oxygen species (ROS) generation in cerebral tissue were found to be higher in aged, compared to young rat. Further decline of those parameters was observed in aged rat brain by the induction of global moderate cerebral ischemia and reperfusion. MLCDP treatment when compared to free or LCDP treatment prevented global moderate cerebral ischemia-reperfusion induced mitochondrial damage as evident ultra structurally and release of cytochrome c (cyt c) from mitochondria into cytosol and protected mitochondria to restore its normal structure and functions.

Molecular physiology of preconditioning-induced brain tolerance to ischemia

Ischemic tolerance describes the adaptive biological response of cells and organs that is initiated by preconditioning (i.e., exposure to stressor of mild severity) and the associated period during which their resistance to ischemia is markedly increased. This topic is attracting much attention because preconditioning-induced ischemic tolerance is an effective experimental probe to understand how the brain protects itself. This review is focused on the molecular and related functional changes that are associated with, and may contribute to, brain ischemic tolerance. When the tolerant brain is subjected to ischemia, the resulting insult severity (i.e., residual blood flow, disruption of cellular transmembrane gradients) appears to be the same as in the naive brain, but the ensuing lesion is substantially reduced. This suggests that the adaptive changes in the tolerant brain may be primarily directed against postischemic and delayed processes that contribute to ischemic damage, but adaptive changes that are beneficial during the subsequent test insult cannot be ruled out. It has become clear that multiple effectors contribute to ischemic tolerance, including: 1) activation of fundamental cellular defense mechanisms such as antioxidant systems, heat shock proteins, and cell death/survival determinants; 2) responses at tissue level, especially reduced inflammatory responsiveness; and 3) a shift of the neuronal excitatory/inhibitory balance toward inhibition. Accordingly, an improved knowledge of preconditioning/ischemic tolerance should help us to identify neuroprotective strategies that are similar in nature to combination therapy, hence potentially capable of suppressing the multiple, parallel pathophysiological events that cause ischemic brain damage.

Permanent, bilateral common carotid artery occlusion in the rat: a model for chronic cerebral hypoperfusion-related neurodegenerative diseases

Chronic cerebral hypoperfusion has been associated with cognitive decline in aging and Alzheimer's disease. Moreover, the pattern of cerebral blood flow in mild cognitive impairment has emerged as a predictive marker for the progression into Alzheimer's disease. The reconstruction of a pathological condition in animal models is a suitable approach to the unraveling of causal relationships. For this reason, permanent, bilateral occlusion of the common carotid arteries (2VO) in rats has been established as a procedure to investigate the effects of chronic cerebral hypoperfusion on cognitive dysfunction and neurodegenerative processes. Over the years, the 2VO model has generated a large amount of data, revealing the 2VO-related pattern of cerebral hypoperfusion and metabolic changes, learning and memory disturbances, failure of neuronal signaling, and the neuropathological changes in the hippocampus. In addition, the model has been introduced in research into ischemic white matter injury and ischemic eye disease. The present survey sets out to provide a comprehensive summary of the achievements made with the 2VO model, and a critical evaluation and integration of the various results, and to relate the experimental data to human diseases. The data that have accumulated from use of the 2VO model in the rat permit an understanding of the causative role played by cerebral hypoperfusion in neurodegenerative diseases. Thorough characterization of the model suggests that 2VO in the rat is suitable for the development of potentially neuroprotective strategies in neurodegenerative diseases.